iMac shutting down, seconds to minutes.
david G -
Went through several suggestions, 2 trouble tickets. Would come up apparently normally, but shut down/power off on its own shortly afterward. Normal included 3 LED's coming up in order, when the back was off, fans came on normally, never saw the red LED for overheating with back off. Couldn't down load the temp monitoring apps because it wouldn't stay up long enough.
Out of all other options I ordered and replaced the power supply. Went pretty well. Greatest difficulty was getting the connector for the ambient light sensor back on. After the replacement, white power light would come on but no screen. With the back off, didn't get past the second LED. After a few minutes, the one fan open to the back will go to a higher speed. Never get to the 3rd LED, or any screen display.
I just received the universal drive adapter I ordered and am about to take out the internal hard drive and try to recover my data to my MacBook. Then replace the iMac.
Not all faults are easily identifiable.
Separately, since at about the same time, my LaCie backup hard drive failed, I'm up a creek with my data. The hard drive is FireWire only, which I thought was going to become more universal. So the backup hard drive became of no value, even if it hadn't failed. Get a backup drive with multiple, common interfaces!